Obruchevellaand other microfossils in the Burgess Shale: preservation and affinity

Abstract

Charles D. Walcott's thin sections of the Middle Cambrian Burgess Shale of British Columbia, Canada, have yielded many specimens of the helically coiled microfossilObruchevella delicata, as well as fragments of the cyanobacteriaMarpoliaandMorania, sphaeromorph acritarchs, and sclerites of the enigmatic metazoanWiwaxia. Obruchevellaof the Burgess Shale displays a spectrum of preservation styles ranging from tangled masses to well-developed helixes. AllObruchevellaspecimens are preserved in three dimensions, which suggests original skeletalization or early post-mortem mineralization of the organism. Morphologic analysis ofObruchevellasupports an affinity with modern helical cyanobacteria. Study of all reported occurrences ofObruchevellaindicates that: 1) the genus has been overly split into seventeen species; 2) no correlation between size and age ofObruchevellaexists; and 3) mostObruchevellaspecimens are tightly coiled and have helix diameters four to six times their filament diameters.